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Definition of Triiodothyronine
Medically reviewed by Min Clinic Staff | Updated: January 2026
Triiodothyronine: A hormone that is made by the thyroid gland. Triiodothyronine has three iodine molecules attached to its molecular structure. It is the most powerful thyroid hormone, and it affects almost every process in the body, including body temperature, growth, and heart rate. Also known as T3 and liothyronine.